big or little u-joint?

I'd go with the big u-joint too. Probably about the same money and stronger. Your only problem is will they be able to cut down and re-use your old driveshaft. The factory ones had a rubber insert inside to absorb harmonics. By the time their the age our cars are that rubber is usually junk and most driveshaft shops won't want to cut one down and reuse it. Once in a while you get lucky and it's re-usable. I recommend a driveshaft loop too. Cheap insurance IMO